EFFECT OF PRETREATMENTS ON AIR‐DRYING PATTERN AND COLOR OF DRIED PUMPKIN (CUCURBITA MAXIMA) SLICES

Abstract

ABSTRACT Effect of pretreatments on air‐drying pattern and color of pumpkin slices was investigated. Fresh, sulfited (1,000 ppm), blanched (100C for 3 min) and osmotically pretreated pumpkins (40, 50 and 60 °Brix) were air dried at 50–80C. Moisture transfer from fresh and pretreated pumpkin was modeled using Fick's diffusion model, and effective moisture diffusivity (m2/s) was calculated. Moisture ratio decreased with increased drying temperature and time. No constant drying rate period was observed in the drying process. Pre‐osmosed pumpkin recorded lower moisture contents and drying rate. Effective moisture diffusivity was in the range of 6.50 E‐10–2.45 E‐09 m2/s. Arrhenius relation with activation energy for moisture diffusion of 24.49–43.27 kJ/mol expressed the effect of temperature on moisture diffusivity. L*, a*, b*, color intensity (ΔE) and chroma (ΔC) values of dried pumpkin increased with increase in drying temperature from 50 to 60C.PRACTICAL APPLICATIONSPumpkin is usually sun dried during the season of production, packaged and rehydrated in water prior to use. However, some problems are associated with the drying of the commodity. Use of pretreatments such as blanching, sulfiting and osmotic dehydration (OD) prior to forced convection air drying would result in minimal quality degradation, savings in energy and, in the case of OD, the production of eat‐out‐of‐hand snack items. The effects of the pretreatment are mainly related to the improvement of some nutritional, organoleptic and functional properties of the product. Also, pretreatments aid the inhibition of enzymatic browning, provide an adjustment of water activity and the achievement of structural, textural and sensory, and other functionalproperties. These properties are obtained with a reduced energy input over traditional drying processes. Air drying following the pretreatment could be adopted for the production of shelf‐stable dried fruit and vegetable commodities with acceptable quality attributes.